This invention concerns processes for bending plastic pipe in which a pipe to be bent is first heated, then placed in an apparatus having a bending pattern and then cooled.
In such well-known processes plastic pipe is first given a preliminary warming in a warm liquid to bring the pipe to a temperature at which it is easier to bend; however, which does not quite place it in a plastic state. Then the pipe is laid, with the help of manual bending, in a plate-like receiving apparatus, which has a groove-shaped indentation in a shape of a desired bending pattern, to retain the still-elastic pipe in its bent form. Together with this apparatus, the pipe is placed in a hot air oven to bring it to a plasticizing temperature. Thereafter, the pipe as well as the receiving apparatus is cooled and finally the pipe is removed from the receiving apparatus. Because the pipe is still in an elastic condition at places where great deformation takes place during bending, tensions build up which are released by plasticizing and which produce a cross-sectional narrowing, thus, often, a flexible core is pulled into the pipe before it is bent to prevent this.
This process to bend plastic pipe is, because of its numerous work steps and corresponding multiplicity of operational devices, requires much space as well as time, and an undue expenditure of man-hours. Between the individual process steps the pipe must be transported to other process apparatus which, particularly for long pipe, can be very inconvenient and require a great deal of space.
It is an object of this invention to provide a process for bending plastic pipe, including various preliminary and subsequent preparation work steps, which is carried out in one apparatus and the bending of the pipe itself results independently of the skill of an operator carrying out the bending operation. Further, it is an object of this invention to provide a process for bending plastic pipe that prevents a detectable appearance of small cross-sectional differences of bent radii at bent positions.